The present invention is related to exercise training devices and methods, more particularly to devices and methods for targeting specific muscle fiber types and/or operating at extrema of a force-velocity-duration space of the athlete using sport specific motions and/or accurately measuring “intensity” of exercise, particularly for the training of athletes requiring leg strength, and especially athletes utilizing bipedal locomotion, and still more particularly to devices and methods for training athletes utilizing bipedal locomotion by targeting specific muscle fiber types and/or operating at extrema of a force-velocity-duration space of the athlete using sport specific motions and/or accurately measuring “intensity” of exercise.
Due to the increasing awareness of the effects of exercise on health and longevity, and due to the increased financial resources associated with professional sports over the past few decades, exercise physiology has been a rapidly growing field of study, and exercise equipment is a burgeoning industry. Yet, with all the resources applied to the design and development of exercise equipment, there is a lack of exercise equipment and monitoring methods designed specifically to allow one to target specific types of muscle fiber, and/or operate at multiple extrema of the force-velocity-duration space (particularly in the course of sport-specific motions, especially sport-specific motions requiring bipedal locomotion), and/or accurately measuring “intensity” of exercise.
In the field of exercise physiology, the mechanical specificity principle states that muscle development for a sport is most beneficial when the training regimens involve muscle exertions at forces and velocities matching those used in the sport. Similarly, the movement specificity principle states that muscle development for a sport is most beneficial when the training regimens involve motions with muscle synchronizations similar to those used in the sport. Exertions providing benefits according to the movement specificity principle therefore comprise a subset of exertions providing benefits according to the mechanical specificity principle. These two principles are the motivation for “sport-specific training,” i.e., training involving sport-specific motions, since that is believed to be the most effective means of improving athletic performance in a particular sport. Although the fitness equipment industry has produced a wide variety of exercise bicycles, rowing machines, stair simulators, elliptical trainers, etc., in general an athlete cannot perform the modes of motion associated with most sports, particularly sports involving bipedal locomotion, on such exercise machines. Therefore, a major obstacle to the practice of sport-specific training is the difficulty of training in a focused manner using the modes of motion involved in a sport.
Even treadmill training of athletes whose sports require running has severe limitations, since the majority of athletes do not engage in bipedal locomotion without direction changes at a constant velocity over long durations (the exception possibly being distance runners). In most sports, athletes are required to accelerate and decelerate, sometimes abruptly, at a variety of velocities, and in a variety of directions. Even the motions performed by a sprinter involve, upon closer inspection, a range of modes. To excel, a sprinter must not only be able to run at a high velocity, but must also be able to accelerate well at the beginning of a sprint, and throughout the entire acceleration portion of the sprint. A particular sprinter might not be able to accelerate well at very low velocities, but may have a high terminal velocity. In contrast, another sprinter might have good acceleration capabilities at low velocities, but may not be able to reach a high terminal velocity. And even in the acceleration phase, a sprinter may have weaknesses in acceleration ability at one or more ranges of intermediate velocities. Therefore, it would be expected that a sprinter would be expected to benefit most by training in regimes where his or her capabilities are weakest.
Another example of the varied mode requirements of an athlete is the defensive end in American football. An effective defensive end must be able to generate a large force with his legs at a low velocity in a forward direction, as well as sideways directions, to force a tackle out of the way at the line of scrimmage. Also, a defensive end must be able to generate large forces with his legs in the forward and sideways directions at intermediate velocities to accelerate when chasing a dodging ball carrier. Furthermore, a defensive end must be able to reach a high terminal velocity when he is required to chase a ball carrier that is running across open field. Therefore, a comprehensive training program for a defensive end must include focused training in each of these exertion regimes.
The apparatus and method of the present invention provide functionalities which allow for concentrated training in the wide range of exertion regimes, thereby making it useful for sport-specific training of an athlete requiring a variety of exercise modes, or for sport-specific training of a variety of types of athletes. Furthermore, the apparatus and method of the present invention can accurately monitor the capabilities of an athlete in all modes of bipedal locomotion motion involved with the athlete's sport. Furthermore, the method and apparatus of the present invention allows for the analysis of exercise performance, regardless of the modes of motion involved, through analysis of force and velocity data associated with the exercise.
It is known in the field of exercise physiology that the type of muscle fiber which is recruited is dependent on the exerted force, the velocity of the motion, and the duration of the activity. It is commonly believed that there are four types of muscle fiber: a single slow-twitch type (type I) and three fast-twitch types (type IIa, type IIb, and type IIx). Following are the hierarchies for the peak contractile velocity (Vmax) and useful exertion period (T) at maximum output of the four types of muscle fiber:Vmax(IIb)>Vmax(IIx)>Vmax(IIa)>Vmax(I),andT(IIb)<T(IIx)<T(IIa)<T(I),According to recent literature, fast and slow-twitch muscle fibers can generate approximately the same amount of peak force. The rate of transition from low force to high force states is apparently seven-fold higher for fast-twitch muscle fibers than for slow-twitch skeletal muscle fibers. Peak isometric (i.e., zero velocity) force is most likely therefore not dependent on muscle fiber type, although a positive correlation does exist between the percentage of fast-twitch muscle fibers in a muscle and the finite-velocity peak force. Therefore, according to methods of the present invention, training regimes of one preferred embodiment target the development of fast-twitch muscle fiber.
Slow-twitch fibers have a high concentration of oxidative enzymes, but low concentrations of glycolytic enzymes and ATPase, and their operation is predominantly powered by aerobic processes. Slow-twitch fibers have a lower maximum velocity Vmax(I) than fast-twitch muscle fibers but, because aerobic processes are renewable due to their re-energization by oxygen-carrying blood flow to the fibers, they have a longer useful exertion period T(I) (i.e., are more resistance to fatigue) than fast-twitch muscle fibers.
In contrast, fast-twitch fibers have higher concentrations of ATPase and glycolytic enzymes, and lower concentrations of oxidative enzymes than slow-twitch fibers. Of the fast-twitch fibers, the type IIb fibers have the lowest concentrations of oxidative enzymes. Type IIb fibers are capable of high contractile velocities, but are unable to maintain these contraction rates for more than a few cycles without a re-energization period. At the other extreme of the fast-twitch fibers is the type IIa fibers which have higher concentrations of oxidative enzymes (although still lower than the concentrations of oxidative enzymes in slow twitch fibers), and lower concentrations of glycolytic enzymes and ATPase (although still higher than the concentrations of oxidative enzymes in slow twitch fibers) than the IIb or IIx fast-twitch fibers. The type IIa fibers have lower contraction velocities than the type IIb fibers, but are partially renewable through aerobic processes and are therefore more resistant to fatigue. Intermediate in its concentrations of oxidative enzymes, and ATPase and glycolytic enzymes, and therefore intermediate in its contractile velocity and endurance between the type IIa and type IIb fibers, is the type IIx fibers, which are relatively small in number.
ATP is the only fuel instantly available in muscles, and the amount of ATP typically stored in the muscles can last for about four or five seconds. Once the ATP is exhausted, other fuels must be converted to ATP before they can be used. The first and most immediately available source for restructuring ATP is creatine phosphate (CP). CP can recharge ATP anaerobically (i.e., without oxygen) for only a short time, typically five or six seconds. When the muscle's reserves of ATP and CP are exhausted, the body must rely on the anaerobic process known as “glycolysis.” In this process, glucose or glycogen is broken down, causing the by-product build-up of lactic acid which is well known for the burning sensation experienced by athletes and rehabilitative patients during exercise. The lactic acid build-up can occur in as little as two minutes. Through training, elite athletes can build an increased tolerance to high levels of lactic acid. However, glycolysis cannot be relied upon for endurance events, even for elite athletes, because the lactic acid will eventually inhibit muscles from contracting. The final metabolic process for generating ATP is the aerobic metabolizing of carbohydrates, fats, and proteins. Unlike anaerobic glycolysis, aerobic mechanisms require at least one to two minutes of hard exercise in order to generate the breathing and heart rate required to deliver enough oxygen to muscle cells. Due to the dependence of the metabolic ATP-generating processes on force, velocity and duration, the apparatus of the present invention is designed to provide the ability to target specific force-velocity-duration regimes and the method of the present invention uses the targeting of specific force-velocity-duration regimes to develop specific metabolic processes.
It is often held that individual muscle fibers contract on an all-or-nothing basis, i.e., only the number of muscle fibers required to supply the required force are recruited, and each recruited muscle fiber exerts all its available contractile force. However, more recent studies show that as the total force exerted by the muscle increases, increasing numbers of fibers are recruited at relatively low firing rates until the majority of fibers have been recruited, and then the firing rates of the fibers increases. The firing rates are controlled by the nervous system, and it is believed that the physiology of the neurons in the muscles and at the neuromuscular junctions is one of the first things to alter during training as the nervous system becomes increasingly adept at complete and rapid activation of the fibers. According to the all-or-nothing theory, an exercise program targeting only the median range of a subject's force and velocity capabilities may fail to produce contractions of all the muscle fibers, leaving some fast-twitch and slow-twitch fibers unaccessed. According to the recent studies on neural control of muscle fiber, an exercise program targeting only the median range of a subject's force and velocity capabilities may fail to produce changes in the neural physiology required to increase the firing rate of the fibers, and therefore will be less than optimal in the development of muscle tissue.
Although widely debated, it is sometimes held in the field of exercise physiology that it is best to train near the center of a subject's force and velocity capabilities so that both fast- and slow-twitch fibers are simultaneously recruited. This exercise methodology may be valid for the rehabilitation or training of a subject who requires medium endurance, medium power, and medium speed. However, the methods of the present invention provide means to focus on extremes of a subject's force and velocity capabilities to provide benefits unobtainable otherwise, as per the aforementioned all-or-nothing theory and the aforementioned recent work on neural control of muscle fibers. Therefore, the present invention includes apparatus and methods which access extremes of a subject's force and velocity capabilities.
Every muscle has two distal ends at which it is anchored to bone by tendons. At an anchor point the muscle can only exert a force in the direction away from that anchor point and towards the opposing anchor point. Therefore, muscle exertion may be categorized into three regimes depending on whether the work performed by the muscle is positive, negative or zero. When a concentric exertion is performed the end-to-end length of the muscle decreases, and the work (which is equal to the vector dot product of the force and the displacement) done is positive since the force is in the same direction as the displacement. For instance, when the body is pushed up away from the ground during a push-up, the triceps are performing concentric exertions. When an eccentric exertion is performed the end-to-end length of the muscle increases, and negative work is done since the exerted force is in the opposite direction to the displacement. For instance, when the body is lowered towards the ground during a push-up, the triceps are performing eccentric exertions. When a static exertion is performed, the end-to-end length of the muscle is constant, and no work is done since the displacement is zero. For instance, when the body is held stationary with the arms partially extended during a push-up, the triceps are performing static exertions. (As discussed in detail below, although no work is performed in a static exertion, physiologically the exertion may require considerable energy and may therefore be a high intensity exertion.) Eccentric exertions are capable of producing larger forces than static exertions, and static exertions are capable of producing larger forces than concentric exertions. Therefore, it is often held that training programs concentrating on eccentric exertions may produce the greatest muscle development.
Generally, complex movements involves both concentric and eccentric muscle exertions. For instance, deceleration during bipedal locomotion to avoid collision, stay “in bounds,” or slow down is a common form of predominantly eccentric movement in sport. It is important to note that not all of the movements of a stride during bipedal deceleration involve eccentric exertions. For instance, the initial movement forward of a backward-extended leg involves concentric exertions of the iliopsoas and the rectus femoris.
Clearly, the functioning of muscle tissue is extremely complex—each muscle has four different types of muscle fibers, the firing of these fibers is determined by duration, velocity and force, as well as the neurological physiology of the neuromuscular junctions, and the muscles can operate in the concentric, eccentric and static exertion mode. Therefore, the apparatus and methods of the present invention are designed to provide sufficient versatility to accurately and efficiently target any exertion mode (i.e., eccentric, concentric or static) and any desired force, duration, and velocity.
According to the conceptual framework of the present invention, it is useful to chart muscle exertions in a mathematical space that includes duration along with the standard variables of force and velocity, i.e., a force-velocity-duration space 200 as depicted in FIG. 3. Furthermore, it should be noted that it is an innovation of the present invention to chart complex modes of motion, such as bipedal locomotion, in such a space 200. In this space 200, the vertical axis represents force, the horizontal axis represents velocity, and the forward-and-to-the-left axis represents duration. The origin O corresponds to a situation where zero force is exerted, the muscle contracts with zero velocity, and no time has elapsed. The region bounded by the zero-velocity surface, the zero-force surface and the zero-duration surface, for which force, velocity and duration are all positive is the “first quadrant” of the space. Surface 202 is a locus of maximal exertions of a muscle for a fixed force-to-velocity ratio. Curve 210 lies in the zero-duration plane and corresponds to the maximal exertion of a well-rested muscle, and the decay of the force and velocity magnitudes on the surface 202 as duration is increased indicates how the muscle fatigues. Dashed line 250 lies on the intersection of the maximum intensity surface 202 with the zero-velocity plane, and therefore represents the maximum exertable static force as a function of time. Similarly, dashed line 251 lies on the intersection of the maximum intensity surface 202 with the zero-force plane, and therefore represents the maximum zero-load velocity as a function of time.
On the zero-time maximal exertion curve 210, point 212 is located where the zero-time maximal exertion curve 210 intersects the force axis. The force value Fmax of point 212 therefore represents the maximum force a muscle can initially exert during a static exertion. On the zero-time maximal exertion curve 210, point 216 is located where the curve 210 intersects the velocity axis. The velocity value Vmax of point 216 therefore represents the maximum velocity with which a muscle can initially contract when there are no opposing forces.
As can be seen from FIG. 3, the zero-time maximal exertion curve 210 is a monotonically decreasing function of duration. Point 211 on the zero-time maximal exertion curve 210 corresponds to the situation where the force applied to the muscle is greater than Fmax, the maximum static force the muscle can exert, and so the velocity is negative and the exertion is eccentric. Similarly, point 217 on the zero-time maximal exertion curve 210 corresponds to the situation where a small force is applied to the muscle in the direction of its contraction, so the velocity of contraction is greater than the maximum zero-force contraction velocity Vmax of the muscle, and so the force is considered to have a negative value.
Different sports or exercise regimens correspond to different regions of the force-velocity-duration space 200 of FIG. 3. For instance, the arms of a power lifter performing a bench press must generate large forces at small and intermediate velocities for relatively short periods of time. Therefore such exertions lie in the region labeled “W” bounded by the dashed line 263, and the training program of a weight lifter should focus on region W to develop fast-twitch, as well as some slow-twitch, muscle fiber. In contrast, the legs of a cyclist need to generate medium velocity and medium force over very long periods. Therefore, such exertions fall in the region between dashed lines 260 and 261 labeled “C,” and the training program of a cyclist should focus on region C to develop the required slow-twitch and fast-twitch muscle fibers. As another example, if a small parachute is attached to a sprinter, then the small impeding force prevents the sprinter from reaching the velocity Vmax, and maximal intensity exertions correspond to the region D bounded by line 262 and the zero-force locus 251. For such exertions, anaerobic, fast-twitch muscle fibers are predominantly recruited during the initial stage, while aerobic, slow-twitch muscle fibers are predominantly recruited during the later stage. As still another example, Tai Chi exercise involves low-force, low-velocity motions over long periods of time, recruiting aerobic slow-twitch muscle fibers and corresponding to a region in the first quadrant along the duration axis of FIG. 3. While this does not fall under the traditional Western rubric of exercise, it is now generally accepted that there are definite therapeutic and rehabilitative benefits of such exercise.
Overspeed training exercises are an important class of exercises which fall outside the first quadrant of the force-velocity-duration space of FIG. 3 in the region where there is an applied negative force (i.e., a force applied to the subject along, rather than against, the direction of motion) resulting in a velocity greater than the maximum velocity Vmax with which the subject can move unassisted. Overspeed exertions are represented by the region around point 217 on the force-velocity-duration space of FIG. 3. Overspeed training exercises target the anaerobic, fast-twitch muscle fibers and, according to the mechanical specificity principal, such exercises are a highly effective means of increasing the maximum velocity Vmax which a subject is capable of achieving. Furthermore, especially for complex movements such as the bipedal locomotion of a sprint, one of the limiting factors in increasing a subject's terminal velocity Vmax is the subject's coordination. Overspeed training overcomes this barrier by allowing the subject to develop coordination in a normally inaccessible velocity regime.
A runner can receive the benefits of overspeed exercise by, for instance, sprinting down an incline. In this case, the force of gravity acts on the runner in the direction of motion, so that the runner can achieve a speed greater than that which he could attain on level ground. Alternatively, a runner can perform overspeed exercise by attaching himself to a tow rope which will tow him forward at a speed greater than that which he could attain unassisted. However, it should be noted that the tow-rope method is somewhat inconvenient, and both of these scenarios for overspeed training are dangerous since muscle failure or loss of balance is likely to result in injury.
The apparatus and method of the present invention allow overspeed training to be accomplished in a much safer and more controlled environment. A first method of overspeed training using the apparatus of the present invention involves reducing the weight of the subject by partially suspending the subject using an overhead harness—since the forces which the subject can exert are unchanged, the reduced effective mass allows greater acceleration during each stride to be achieved, and therefore a greater maximum velocity to be achieved. This is termed “reduced-weight overspeed training.” One advantage of reduced-weight overspeed training is that the overspeed harness prevents the subject from injuring himself if, or when, muscle failure or loss of balance occurs. Another advantage of reduced-weight overspeed training is that the decrease in weight reduces the forces of impact applied to the leg joints. In contrast, overspeed training accomplished by running down an actual incline increases the forces of impact applied to the leg joints, therefore increasing the risk of injury to the leg joints.
Another method of overspeed training using the apparatus of the present invention involves applying a forward ‘towing’ force to the subject using a harness mounted on a front strut of the apparatus. This is termed “simulated tail wind overspeed training,” since a tail wind on a runner produces a force in the same direction. An additional method of overspeed training using the apparatus of the present invention involves setting the surface angle of the revolving belt to a negative angle, simulating a declined plane. This is termed “simulated downhill overspeed training.” These two overspeed training methods also force the subject to run at a velocity greater than that which the subject can reach on level ground without assistance. It should be noted that also using the fore and aft harnesses in the reduced-weight overspeed training mode or the simulated downhill overspeed training mode provides the benefits of fixing the longitudinal position of the subject and therefore allowing more accurate monitoring of the performance of the subject, and providing additional support if, or when, there is muscle failure or loss of balance. Also using the overhead harnesses in the simulated tail wind overspeed training mode or the simulated downhill overspeed mode provides additional support if, or when, there is muscle failure or loss of balance.
According to the present invention, another important advantage of over-speed training is based on an intent hypothesis of muscle fiber recruitment. According to this hypothesis, the intent of the subject may play a crucial role in determining which muscle fibers are recruited in a muscle exertion. For instance, a weight lifter's intent in a clean-and-jerk maneuver to produce a large, short-duration force may play an important role in the recruitment of the anaerobic, fast-twitch muscle fibers used in the maneuver. Similarly, a sprinter's intent to reach maximum velocity as quickly as possible may allow a greater percentage of anaerobic fast-twitch muscle fiber to be recruited in the initial acceleration phase of a sprint where the velocity of the subject is low. Additionally, the sprinter's intent to reach and/or maintain a speed greater than his unassisted maximum velocity Vmax may allow a greater percentage of anaerobic, fast-twitch muscle fiber to be recruited than in exercises where the subject intends to perform within the first quadrant of the force-velocity-duration space. Therefore, training regimens where the subject intends to perform outside the first quadrant of the force-velocity-duration space would produce development of the anaerobic, fast-twitch muscle fibers unequaled by any exercises within the first quadrant of the force-velocity-duration space.
While the intent hypothesis seemingly contradicts the mechanical specificity principle, it should rather be viewed as a supplemental theory addressing the complicating effects of the mind on muscle fiber recruitment. Furthermore, the intent hypothesis may play an important role in addressing how muscle fibers are recruited at the very beginning of a muscle contraction when the target velocity or force has not yet been reached. Because of the accuracy and versatility of the method and apparatus of the present invention, the method and apparatus of the present invention facilitates research regarding the intent hypothesis.
An accurate measure of the degree of muscular exertion would allow the gauging and monitoring of an athlete's performance, and would therefore play an important role in training programs. Although it is commonly assumed that power output (defined as the vector dot product of the force applied by the subject and the velocity) is a useful variable in measuring performance, the use of this variable is actually problematic. For example, consider the case of a weight lifter holding a barbell completely stationary overhead. Common sense tells us that the weight lifter is exerting a substantial amount of effort to support the weight. Yet, since the velocity of the barbell is zero, the power output is zero.
Some attempts to measure muscle exertion have used the electromyograph, an instrument which determines muscle activity by detecting the depolarization of muscle cells upon neural stimulation by measuring changes in voltage across surface electrodes or fine wires inserted into the target muscle. However, electromyographs are generally considered to provide only rough estimates of muscle activity due to the unpredictability of the conductance of muscle and skin tissue.
In the field of exercise physiology, “intensity” of exercise is generally defined as the ratio of the actual load or weight used in an exercise divided by the maximum load or weight which a subject can move through a single cycle of the exercise. However, according to the present invention the intensity is defined as the ratio of the exertion level performed divided by the maximum exertion which a subject is capable of at that moment. Therefore, a bench press of 5 kg may require only a minimum of intensity on the first cycle of motion, but a considerable intensity after 40 cycles.
The difference between power, in the Newtonian mechanics sense of the word, and intensity, as per the present invention, is highlighted by a comparison of the constant-intensity curves of FIG. 7 and the constant-power curves of FIG. 8. FIG. 7 shows three zero-time constant intensity curves: a high intensity curve 410, a medium intensity curve 430, and a low intensity curve 440. As time goes on and the subject tires, the high, medium and low intensity curves 410, 430 and 440 collapse towards the origin O to provide finite-time high, medium and low intensity curves 460, 470 and 480. It should be noted that the constant intensity curves 410, 430, 440, 460, 470 and 480 are concave upwards and cross both the velocity and force axes. In contrast, the constant power curves 510, 515 and 520 of FIG. 8 are defined by the equation of a hyperbola, i.e.,F=P/v, where P is power. Therefore, although the constant power curves 510, 515 and 520 are also concave upwards like the constant intensity curves 410, 430, 440, 460, 470 and 480, the constant power curves 510, 515 and 520 never cross the force or velocity axes.
Generally, trainers and coaches must rely upon data collected from relatively imprecise performance tests in their analyses of athletes. While existing exercise equipment may provide crude means for measuring force, speed, duration, and/or power, they do not provide an accurate means for measuring exercise intensity. In addition, there is a wide variety of characteristics which may be used to describe or categorize an athlete, such as height, weight, muscle mass, muscle fiber ratios, respiratory and cardiovascular capability, flexibility, etc. Therefore, the design of appropriate training programs for athletes, the comparison of athletes, and the assignment of optimal roles for athletes from a team's talent pool are clearly complicated and difficult tasks.
The ability to accurately measure variables associated with the performance of an athlete according to the present invention offers trainers and coaches a much higher degree of accuracy in understanding the capabilities of an athlete, and in comparing athletes. Detailed analyses may even differentiate between the capabilities of an athlete's fast-twitch and slow-twitch muscle fibers. Furthermore, using such data, especially when taken over the course of a training program, allows for the execution of analyses to estimate the potential for development of the athlete, and to tailor subsequent training programs to the particulars of the athlete's developmental capabilities and the requirements of the sport for which the athlete is training.
It is important to note that standard exercise devices, such as treadmills, are generally designed for muscle exertions requiring positive force and velocity (i.e., exertions where the virtual displacement of the subject is in the direction opposite the force applied by the subject). In contrast, the apparatus and method of the present invention also allows access to training regimes with negative velocity (i.e., exertions where the virtual displacement is in the direction opposite the force exerted by the subject on the apparatus), thereby allowing access to the advantages involved in eccentric exertions. Also, the apparatus and method of the present invention allows access to training regimes with negative force (i.e., exertions where apparatus applies a force on the subject in the direction of the virtual displacement), thereby allowing access to the advantages involved in overspeed exertions. It should also be understood that standard exercise devices are typically designed to operate in a time-invariant fashion. In contrast, the apparatus and method of the present invention allows for time-dependent force and velocity parameters. Having time-dependent force and velocity parameters provides a versatility which allows, for instance, an exercise program where force and velocity follow the time-dependent behavior described by the maximal intensity surface 202 of FIG. 3, i.e., an exercise program which allows force and velocity to be modified as functions of time so that exercises can be conducted until exhaustion and/or a full range of muscle fibers are accessed.
Currently-available exercise bikes have a number of deficiencies with regards to the training of athletes for bipedal locomotion. Such exercise bikes are generally best suited for the training of endurance athletes, where long durations and sub-maximal forces are prevalent, and slow-twitch muscle fibers are predominantly recruited. For instance, the exercise bike of Scholder et al. (U.S. Pat. No. 5,256,115) allows the pedal resistance to be adjusted, but provides no means of immovably securing the subject while forces are applied to the pedals. Because the legs are generally much stronger than the arms and hands, the forces which can be exerted by the legs on exercise bikes such as Scholder et al. are limited to some degree by the strength with which the subject can grip the handle bars. This is demonstrated by noting that the low-velocity acceleration of a sprinter is greater than that of bicyclist, since the sprinter can exert forces at low velocities near Fmax, whereas a bicyclist cannot. Additionally, the unmonitored motions of the body of the bicyclist result in an uncertainty in the magnitude of the applied forces by the subject, even if the forces on the pedals were to be precisely monitored. Furthermore, since exercise bikes require a circular, or in some cases elliptical, motion of the feet, they are an imperfect emulation of the motions associated with normal human bipedal locomotion. Therefore, according to the movement specificity principle, exercise bikes are not well-suited for the training of athletes requiring a high level of performance of bipedal locomotion. Another disadvantage of exercise bikes is that they provide no means of exercising muscles in an eccentric fashion. Since eccentric muscle contractions are capable of producing forces greater than the maximum zero-velocity force Fmax, training regimens involving eccentric exertions may provide valuable benefits. It should also be noted that currently-available exercise bikes do not have means for altering the velocity as an arbitrary function of the applied forces, or altering the resistance forces as an arbitrary function of the velocity of the pedals.
Many of the disadvantages of currently-available exercise bikes also apply to currently-available staircase emulators, such as in the one described by Potts in U.S. Pat. No. 4,687,195. It should be noted that Potts allows for the adjustment of the speed of a revolving inclined staircase but, given that it has no means of immovably securing the subject, it does not allow a subject to exert a force greater than the subject's weight so, generally, the exerted force will be substantially less than the maximum zero-velocity force Fmax which a subject is capable of. Also, because the motions of the body of the subject are unmonitored, the magnitude of the forces exerted by the subject cannot be determined even if the forces on the staircase are precisely monitored. Furthermore, it should be noted that staircase emulators do not allow any variation in stride length or in the angle from horizontal in which the bipedal locomotion occurs, so, according to the movement specificity principle, they are of limited value for the training of athletes requiring a high level of bipedal locomotion performance. Additionally, staircase emulators are not operable in reverse, and so cannot provide means for eccentric exercises where there is the capability of producing forces greater than the maximum zero-velocity force Fmax which a subject is capable of, thereby obtaining the valuable training benefits associated therewith. It should also be noted that currently-available staircase emulators do not have means for altering the velocity as an arbitrary function of the applied forces, or altering the resistance forces as an arbitrary function of the velocity, and the maximal speeds of such devices do not approach the terminal velocity of most athletes.
Many of the disadvantages of currently-available exercise bikes and staircase emulators also apply to treadmill devices, such as in the motorized treadmill apparatus described by Skowronski in U.S. Pat. No. 5,382,207. It should be noted that the treadmill device of Skowronski does not provide means for immovably securing the subject. Therefore, since the legs are generally much stronger than the arms and hands, the forces which can be exerted by the legs are limited by the strength with which the subject can secure his position on the treadmill by gripping whatever surfaces are provided. It should be noted that although the plane of the treadmill may be inclined upwards, generally the angle of incline is not sufficient to allow the exerted forces to approach the maximum zero-velocity force Fmax. Additionally, the motions of the body, which are unmonitored, result in an uncertainty in the magnitude of the forces exerted by the subject, even if the forces on the treadmill were to be precisely monitored. Also, most treadmills have a maximum speed of approximately 10 miles per hour, and are therefore inadequate for the training of sprinters. While some treadmills also allow the conveyor surface to be given a downhill slant, it should be noted that running downhill may produce dangerous increases in the stresses incurred by the leg joints. Furthermore, since treadmills generally do not provide means for having the belt move in the reverse direction, they cannot target eccentric exertions of the muscles. It should also be noted that currently-available treadmills do not have means for altering the velocity as an arbitrary function of the applied forces, or altering the resistance forces as an arbitrary function of the velocity of the belt.
In “The Mechanical Efficiency of Treadmill Running Against a Horizontal Impeding Force,” by B. B. Lloyd and R. M. Zacks, published in the Journal of Physiology, volume 223, pages 355-363, 1972, the mechanical efficiency of bipedal locomotion is measured by monitoring the oxygen consumption of a subject running on a treadmill rotating at a constant speed, with the subject under the influence of a horizontal impeding force. It is important to note the details of the apparatus of FIG. 1 of Lloyd, and contrast this apparatus with the system of the present invention. In Lloyd a horizontal impeding force is provided by a restraining weight which is strung over a pulley and connected to a harness on the subject. The subject maintains his position on the treadmill by accelerating when he notices that he is moving towards the back of the treadmill and decelerating when he notices that he is moving closer to the front of the treadmill. Because the subject is not strictly fixed in one location, the position is known only to within the constraints of the length of the treadmill and the slack available in the air recovery tube, and fluctuations in the velocity are not determinable, i.e., it is only the time-averaged velocity of the subject is known. Furthermore, oxygen consumption is only useful in monitoring steady-state aerobic processes. Therefore, the apparatus of Lloyd only permits the study of steady state scenarios. Transient information cannot be monitored using Lloyd's apparatus since the transient information is lost due to the inherent time averaging which occurs. It should also be noted that the treadmill of Lloyd does not include means for altering the velocity as an arbitrary function of the applied forces, or altering the resistance forces as an arbitrary function of the velocity of the conveyor.
It should be noted that the apparatus of Lloyd does not actually produce a constant horizontal impeding force. When the subject runs at a velocity greater than the velocity of the treadmill, he will move forward relative to the ground and move the mass upwards, and so the force applied to the subject will be greater than the weight of the mass. Similarly, when the subject runs at a velocity less than the velocity of the treadmill, he will move backwards relative to the ground and allow the mass to drop, and the force applied to the subject will be less than the weight of the mass. Additionally, if the mass drops rapidly it may somewhat stretch the tether and bounce back upwards, or the mass may tend to swing back and forth. Either of these situations produces an unpredictably varying horizontal impeding forces. (Since, according to Newton's laws, a body will stay fixed in position only if the net force on the body is zero, it can be determined that the sum of forces acting on the subject of Lloyd, i.e., the force exerted by the harness and the force exerted by the treadmill, does not generally sum to zero.) Also, because the subject does not have any additional harnessing, the mass of the restraining weight must be small enough that there is little danger of causing the subject to fall backwards.
In summary, deficiencies and disadvantages of some or all of the prior art exercise apparatuses, in view of the above discussions of the prior art and the description of the present invention below, include:                exertions near, at or beyond the maximum zero-velocity force Fmax cannot be performed;        exertions near, at or beyond the maximum zero-force velocity Vmax cannot be performed;        regions outside the first quadrant of the force-velocity-duration space cannot be accessed;        exercises throughout the first quadrant of the force-velocity-duration space cannot be performed;        exercises involving eccentric and/or a combination of concentric and eccentric exertions cannot be targeted;        a variety of specific muscle fiber types cannot be targeted;        fast-twitch muscle fibers cannot be targeted;        exercises do not involve bipedal locomotion;        training for improved acceleration at a selected velocity cannot be achieved;        exercises involving those motions utilized in an athlete's particular sport cannot be achieved;        exercises in most or all of the following modes of bipedal locomotion (acceleration, deceleration, lateral acceleration and eccentric exertions) cannot be achieved;        simulation of the forces and velocities experienced by a subject during a sprint cannot be achieved;        simulation of a variety of gravitational conditions and/or a range of weights of the subject cannot be achieved;        bipedal locomotion on surfaces having a variety of inclinations cannot be simulated;        the forces exerted by the subject and the velocity of the subject relative to the conveyor cannot be accurately monitored;        a truly isokinetic (i.e., constant velocity) mode of operation cannot be achieved;        a truly isotonic (i.e., constant force) mode of operation cannot be achieved;        a truly constant load mode of operation cannot be achieved;        the velocity cannot be controlled while the applied force is monitored;        the resistance force cannot be controlled while the velocity is monitored;        the resistance force and velocity cannot be independently controlled as a function of time;        the velocity cannot be altered as an arbitrary function of the applied forces;        the applied force cannot be altered as an arbitrary function of the velocity;        exercise intensity is not determined;        exercise programs which follow the time-dependent behavior of a maximum intensity locus on the maximum intensity surface cannot be provided; and        exercises cannot be performed over the full range of intensities.        